1) Field of the Invention
This invention generally relates to an antifreeze/coolant concentrate. More particularly, this invention relates to an antifreeze/coolant concentrate which is capable of effectively inhibiting cavitation damage in a cooling system for a vehicle.
2) Prior Art
Vehicle engine cooling systems include metal portions made of aluminum, aluminum alloy, cast iron, steel, brass, solder and/or copper. These metal portions are prone to corrosion by contacting water and/or air contained in coolant water (coolant) which circulates through cooling systems. In order to prevent metal corrosion, an antifreeze/coolant concentrate or other concentrates containing metal corrosion inhibitors are blended in coolant in an appropriate concentration.
Metal portions of a cooling system can be damaged by other causes as well. Due to air (oxygen) unavoidably dissolved in coolant, so-called "cavitation" is generated in circulating coolant from local pressure differences, which will considerably damage metal portions, especially iron or cast iron portions of cooling systems. Such cavitation can also be generated by vibration of cooling systems. Generally, larger vehicles produce more vibration than smaller vehicles.
A nitrite is often contained in conventional antifreeze/coolant concentrates in an attempt to inhibit such cavitation damage in cooling systems. It is generally accepted that a nitrite in coolant provides a protective layer on metal surfaces, specifically on iron surfaces, and protects the metal (iron) portions from cavitation damage.
Whatever the actions may be, it is proved that a nitrite is capable of very effectively inhibiting cavitation damage in a cooling system. However, nitrites often produce harmful nitrosoamine by reacting with an amine salt or salts in coolant, which is a carcinogenic substance. Since no other effective cavitation damage inhibitors were known, antifreeze/coolant concentrates containing a "substantial" amount of nitrite have continually been used in coolant, though their use is not altogether advisable from the foregoing point of view.
Accordingly, it is an object of the present invention to provide an antifreeze/coolant concentrate containing no nitrites, which can still effectively inhibit cavitation damage onto metal portions of a cooling system for a vehicle engine, especially for a large vehicle engine where substantial vibration is generated.
The foregoing object of the present invention should be construed as including an object to provide an effective cavitation damage inhibiting antifreeze/coolant concentrate without necessity to contain so much nitrite as was conventionally regarded necessary to effectively inhibit cavitation damage so that production of environmentally harmful nitrosoamine in coolant may be substantially suppressed.